refactor(ai): improve error handling and stop reason types

- Add 'aborted' as a distinct stop reason separate from 'error'
- Change AssistantMessage.error to errorMessage for clarity
- Update error event to include reason field ('error' | 'aborted')
- Map provider-specific safety/refusal reasons to 'error' stop reason
- Reorganize utility functions into utils/ directory
- Rename agent.ts to agent-loop.ts for better clarity
- Fix error handling in all providers to properly distinguish abort from error

packages/ai/src/event-stream.ts

@@ -1,82 +0,0 @@
-import type { AssistantMessage, AssistantMessageEvent } from "./types.js";
-
-// Generic event stream class for async iteration
-export class EventStream<T, R = T> implements AsyncIterable<T> {
-	private queue: T[] = [];
-	private waiting: ((value: IteratorResult<T>) => void)[] = [];
-	private done = false;
-	private finalResultPromise: Promise<R>;
-	private resolveFinalResult!: (result: R) => void;
-
-	constructor(
-		private isComplete: (event: T) => boolean,
-		private extractResult: (event: T) => R,
-	) {
-		this.finalResultPromise = new Promise((resolve) => {
-			this.resolveFinalResult = resolve;
-		});
-	}
-
-	push(event: T): void {
-		if (this.done) return;
-
-		if (this.isComplete(event)) {
-			this.done = true;
-			this.resolveFinalResult(this.extractResult(event));
-		}
-
-		// Deliver to waiting consumer or queue it
-		const waiter = this.waiting.shift();
-		if (waiter) {
-			waiter({ value: event, done: false });
-		} else {
-			this.queue.push(event);
-		}
-	}
-
-	end(result?: R): void {
-		this.done = true;
-		if (result !== undefined) {
-			this.resolveFinalResult(result);
-		}
-		// Notify all waiting consumers that we're done
-		while (this.waiting.length > 0) {
-			const waiter = this.waiting.shift()!;
-			waiter({ value: undefined as any, done: true });
-		}
-	}
-
-	async *[Symbol.asyncIterator](): AsyncIterator<T> {
-		while (true) {
-			if (this.queue.length > 0) {
-				yield this.queue.shift()!;
-			} else if (this.done) {
-				return;
-			} else {
-				const result = await new Promise<IteratorResult<T>>((resolve) => this.waiting.push(resolve));
-				if (result.done) return;
-				yield result.value;
-			}
-		}
-	}
-
-	result(): Promise<R> {
-		return this.finalResultPromise;
-	}
-}
-
-export class AssistantMessageEventStream extends EventStream<AssistantMessageEvent, AssistantMessage> {
-	constructor() {
-		super(
-			(event) => event.type === "done" || event.type === "error",
-			(event) => {
-				if (event.type === "done") {
-					return event.message;
-				} else if (event.type === "error") {
-					return event.partial;
-				}
-				throw new Error("Unexpected event type for final result");
-			},
-		);
-	}
-}